Round composite rods are generally made by extrusion or pultrusion. However, in the case of forming composite rods containing high-modulus high-strength filaments such as boron, silicon carbide, and graphite filaments, the prior art process becomes uneconomical. One important reason is that high-modulus high-strength filaments are generally first placed into a composite in a form of flat strips or sheets. Typically, a resin matrix or metal matrix composite contains a monolayer of filaments which have been laid up so that they lie substantially parallel to each other in a side-by-side relationship. The matrix is then cast around the filaments and either fully cured or partially cured into strips of composite materials or sheets of composite material. At times, such composite materials contain mulit-layers of filaments, either uniformly aligned or randomly aligned.
Boron and silicon carbide filaments are hard materials. The replacement costs of extrusion or pultrusion dies would be very high.
Heretofore, narrow strips of such composite materials have been used as reinforcements in a variety of products, but most notably in tennis rackets. It was then determined that performance could be improved if the composite reinforcement for tennis rackets was in the shape of a round rod rather than a flat strip. Given the conventional way of making such composite materials as flat structures, the problem was to convert such flat structures, and particularly flat strips, into round rods.
It is an object of the invention to provide a method of forming a round composite rod from a flat composite strip which avoids the limitations and disadvantages of prior art devices.
It is another object of the invention to provide a process of forming a round composite rod from a flat strip in a simple and facile manner.
It is yet another object of the invention to provide a method of forming a round composite rod from a flat composite strip to the sole use of heat without the use of dies of any type.
It is yet another object of the invention to provide a method of forming a round composite rod from a flat composite strip wherein the conversion can be made to conform with close tolerance requirements for the round composite rod.
In accordance with the invention, a method of forming a round composite rod from a flat composite strip comprises vertically suspending a flat composite strip containing longitudinally aligned filaments within a matrix, said matrix being capable of being softened. The temperature of a substantial length of the composite strip is raised to the transition temperature and maintained at the transition temperature until the cross section of the composite assumes a substantially round configuration. Finally, the round composite is solidified.
The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which: